So I guess my question is what is actually happening here? My 06 that I just gutted the cats on and used spacers for the downstream o2s also has a steady upstream .3 and .6 volt readout which seems to be hybrid/anomaly of some sort that other xterra, frontier and pathfinder owners have reported also having. All I have ever seen is either the standard switching .1-.8 volt o2 or the newer wide bands which use a much higher voltage or display on mA I believe. I know using he same obd2 scanner between my two xterra shows my 06 to have the steady .3/.6 but my ‘11 pro4x shows that it is using a/f widebands. So why is it that our x’s do this? Technically the average of those two numbers is .45 volts which is what they say upstream should average out to but that is when they are switching. It’s supposed to be an average for the bank, not an average between the banks. This also made me question my understanding of what triggered a p0420/30. I thought the ecu was looking for a minimum difference between the upstream average and the downstream constant. Meaning it was increasing the amount of o2 in the downstream by a specific percent. Which would mean the downstream would fluctuate too but once I learned downstreams are supposed to be steady to indicate a working cat it makes me think that it looks for a certain target downstream rate meaning no matter what goes in a specific mixture comes out. Even if the downstream volts are higher than the upstreams, which is the case of the .3volt upstream bank. I am getting both p0420/30 codes even with the spacers and my values up and down match each other which makes sense as the spacer still allows full access of the exhaust gasses to the sensor tip. So the spacers really do nothing. Someone please help me understand all this as the upstream values and what triggers the p0420/30 has now got me all tirned around.